Animate dropdowns

All of our dropdowns should have a nice, smooth animation.

See details and an example of the proposed animation here: https://docs.gitlab.com/ce/development/ux_guide/animation.html#dropdowns

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Update

We added support for animation to most dropdowns with !8419 (merged), but there are still a few dropdowns which lack animation support as mentioned here. Here's a list of dropdowns which lack animation support that we can try and add support for;

  • Issues and MR filter search dropdown

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  • All select2 based dropdowns

  • Comment/Discussion toggle dropdown

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  • Browser native dropdowns (convert them to rich dropdowns?)